[SWODY1] SWODY1

[Severe Weather Outlook Day 1]

ACUS01 KWNS 191951
SWODY1
SPC AC 191949

DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
0249 PM CDT WED APR 19 2006

VALID 192000Z - 201200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN AND TONIGHT
ACROSS MUCH OF TX THROUGH THE EASTERN GULF STATES....

BLOCK REMAINS ESTABLISHED IN BELT OF FLOW EXTENDING ACROSS THE NORTH
CENTRAL U.S. INTO THE WESTERN ATLANTIC.  MODELS SUGGEST DEEP CLOSED
LOW OFF THE NORTH ATLANTIC COAST WILL MOVE LITTLE THROUGH LATE
TONIGHT...BUT HIGH CENTER MAY BEGIN TO WEAKEN OVER EASTERN ONTARIO
AS UPSTREAM CLOSED LOW GRADUALLY SHIFTS EAST OF THE DAKOTAS INTO THE
UPPER MISSISSIPPI VALLEY.  THIS IS EXPECTED MOSTLY IN RESPONSE TO A
SIGNIFICANT IMPULSE PIVOTING AROUND ITS SOUTHERN/EASTERN PERIPHERY. 
AMPLIFYING UPSTREAM TROUGH OVER THE EASTERN PACIFIC WILL REMAIN WELL
OFFSHORE...BUT MAY BE RESPONSIBLE FOR FORCING CONTINUED EASTWARD
ACCELERATION OF CLOSED LOW/TROUGH ACROSS THE SOUTHERN PLATEAU LATE
THIS AFTERNOON AND TONIGHT.  THIS IMPULSE APPEARS TO BE PRECEDED BY
ANOTHER WEAKER SHORT WAVE TROUGH...WHICH IS PROGGED TO LIFT ACROSS
THE TEXAS BIG BEND REGION THROUGH THE ARKLATEX BY 12Z THURSDAY.

...TENNESSEE VALLEY/GULF STATES...
A BROAD WEAK SURFACE LOW...ROUGHLY NEAR INTERSECTION OF CONVECTIVE
OUTFLOW BOUNDARY AND SLOWLY ADVANCING COLD FRONT...NOW APPEARS
CENTERED ACROSS NORTHWEST ALABAMA/SOUTHERN MIDDLE TENNESSEE.  THIS
FEATURE HAS BECOME FOCUS FOR STRONGEST DESTABILIZATION...WHICH SEEMS
LIKELY TO LEAD TO FURTHER VIGOROUS CONVECTIVE DEVELOPMENT LATE THIS
AFTERNOON.  

LATEST OBJECTIVE ANALYSIS SUGGESTS MIXED LAYER CAPE IS NOW IN EXCESS
OF 3000 J/KG ALONG/SOUTH OF THE BOUNDARIES...ACROSS MUCH OF NORTHERN
MISSISSIPPI/NORTHERN ALABAMA INTO WEST CENTRAL GEORGIA.  THIS IS
BENEATH 30 TO 40 KT WESTERLY MID-LEVEL FLOW...WHICH IS CONTRIBUTING
TO SUFFICIENT SHEAR FOR SUPERCELLS.  MID/UPPER FORCING IS
UNCERTAIN...BUT CAPPING APPEARS WEAK ENOUGH TO ALLOW FOR CONTINUED
RAPID DEVELOPMENT OF THUNDERSTORMS THIS AFTERNOON WITH ADDITIONAL
HEATING AND PERSISTENT LOW-LEVEL CONVERGENCE.  LARGE CONVECTIVE
CLUSTER MAY EVENTUALLY EVOLVE...AND DEVELOP EAST SOUTHEASTWARD
THROUGH THE EASTERN GULF STATES.  THIS WILL BE ACCOMPANIED BY A RISK
FOR DAMAGING WINDS AND HAIL...SOME OF WHICH MAY BECOME QUITE
LARGE...THROUGH EARLY EVENING.

...TEXAS...
LEAD IMPULSE IS ALREADY SUPPORTING VIGOROUS CONVECTIVE DEVELOPMENT
SOUTH OF THE TEXAS BIG BEND...AND ACTIVITY MAY EVENTUALLY DEVELOP
ALONG SURFACE FRONT SOUTH OF DEL RIO INTO THE SAN ANTONIO AREA ONCE
CAP WEAKENS.  IF THIS OCCURS...VEERING LOW-LEVEL WIND FIELDS WITH
HEIGHT BENEATH MODERATE WEST SOUTHWESTERLY MID/UPPER FLOW WILL BE
SUFFICIENT FOR SUPERCELLS IN ENVIRONMENT WITH MIXED LAYER CAPE IN
EXCESS OF 2000 J/KG.  THIS ACTIVITY MAY DIMINISH DURING THE EVENING
AS INHIBITION INCREASES WITH LOSS OF SURFACE HEATING...BUT WARM
ADVECTION NORTH OF FRONT IS EXPECTED TO SUPPORT INCREASING
THUNDERSTORMS ACROSS CENTRAL INTO NORTHEAST TEXAS.  CAPE FOR PARCELS
BASED IN MOIST LAYER ABOVE FRONTAL INVERSION IS EXPECTED TO BE MORE
THAN SUFFICIENT TO SUPPORT A LARGE HAIL THREAT.

...LWR OH VLY THROUGH UPPER GREAT LAKES...
FORCING ALONG WHAT IS LEFT OF OCCLUDED SURFACE FRONT IS ALREADY
SUPPORTING AN INCREASE IN THUNDERSTORMS ACROSS PARTS OF CENTRAL/
EASTERN WISCONSIN.  ADDITIONAL ACTIVITY APPEARS POSSIBLE LATER THIS
AFTER AND EARLY EVENING...SOUTHWARD INTO PARTS OF ILLINOIS AND
INDIANA...WHERE SHEAR MAY CONTINUE TO BECOME MORE FAVORABLE FOR
UPDRAFT ROTATION.  HOWEVER...OVERALL CONVECTIVE POTENTIAL/ SEVERE
THREAT SEEMS LIKELY TO REMAIN LIMITED DUE TO LACK OF MORE FAVORABLE
DESTABILIZATION.

..KERR.. 04/19/2006